This invention relates generally to compositions containing carbon nanotubes for protection from exposure to harmful ultraviolet radiation and, in particular, to sunscreen compositions containing carbon nanotubes.
1. Field of the Invention
2. Description of the Background
Although exposure to the sun's UV rays is said to be the most important factor in the cause of skin cancers, about 70 percent of American adults do not use sun-protection measures. Currently available formulations provide significant protection from the UVB portions of the spectrum; however, few commercial products offer complete UVA/UVB protection. While UVB radiation accounts for most of the sunburn damages, UVA is responsible for deeper damage to melanocytes and the ensuing melanoma. Incomplete UV blockage precludes full protection from DNA damage and immunosuppression, both of which are induced by UV radiation. In addition, most formulations that block UVA contain irritants that lead to allergic reactions or may develop into toxic agents upon exposure to UV radiations.
Preliminary work in our laboratories has confirmed that multiwall carbon nanotubes (MWNT) effectively block UV transmission in the range from 290 to 400 nm. In the field of material science, carbon nanotubes offer physical properties (such as thermal and electrical conductivity, and tensile strength) that make it suitable in a multitude of applications. We propose to take advantage of the light absorbing properties of carbon nanotubes to develop a sunscreen/sunblock formulation offering (1) complete shielding from UVAs and UVBs and (2) order of magnitude improvement over current products for protection from associated DNA damage and immunosuppression. In addition, potential toxicities associated with the topical application of carbon nanotubes will be identified and eliminated to develop not only a sunscreen with no adverse allergic reactions but also an efficient method of nanotube incorporation into safe, effective commercial products.
The plan will lead to the development of a sunblock formulation that can be used commercially with order of magnitude improvement in UVA and UVB protection over current off the shelf products, with protection from UV-induced immunosuppression, and with no adverse allergic or photoallergic reactions. Phase I will focus on development of a novel nanotube filter in a sunscreen/sunblock vehicle capable of full UVA/UVB blocking. The carbon nanotube suspensions will allow us to initiate further studies into the toxicities of single walled carbon nanotubes (SWNT) in order to eliminate this pitfall and provide a safe, effective method for SWNT incorporation into commercial products. Phase II will consist of clinical studies to determine the efficacy of the formulation to protect against the damaging effects of UV radiation including the immunomodulation properties of SWNT present in a sunscreen. Validation of the sunblock formulation will prove its efficacy for use in various cosmetic products for which sunblocking properties represent an added marketing advantage.
Cancer of the skin is the most common of all cancers in the United States, comprising over half of all cancer diagnoses. As seen in FIG. 1, the incidence of skin cancer in the U.S. has been rising at an epidemic rate, more than doubling itself in the female population and nearly tripling itself in the male population since 1973. In 2001, one million new cases of non-melanoma skin cancer and 51,400 new cases of melanoma skin cancer were reported in the U.S. While melanoma skin cancer represented only 5 percent of all skin cancers in the U.S. in 2001, it accounted for 80% of all skin cancer deaths (equating to approximately 7,800 deaths per year).
There are three main types of skin cancer: (1) melanoma, (2) basal-cell carcinoma, and (3) squamous-cell carcinoma, the latter two being also known as non-melanoma skin cancers. Basal cell carcinoma is normally not lethal but may spread to the bone. Squamous-cell carcinoma can be lethal if not detected early and treated. The deadliest of the skin cancers is by far melanoma. Melanomas spread quickly from skin cells to other organs, most notably the liver, lungs, bones, and brain.1 Ultraviology B (UVB) radiation (280 to 320 nm) has been implicated in the development of non-melanoma and melanoma skin cancers. Ultraviolet A (UVA) radiation (320 to 400 nm) has been shown to exacerbate the detrimental effects of UVB and according to recent studies, may also have a direct effect on melanoma development.2 UVC radiation (100 to 280 nm) does not pose a threat as its ray cannot penetrate earth's atmosphere. Clearly, sunscreen formulations must be capable of blocking both UVA and UVB to achieve maximum effectiveness and eliminate the risk of skin cancer development.
The penetration of UV thorough the skin varies from 0.1–1.0 mm depending on the intensity and wavelength. Excessive exposure to UVB, which exhibits shorter wavelengths than UVA, usually results in topical sunburn.3 This is clinically known as erythema and first appears as reddening, initially at about 2–6 hours after exposure and increasing in intensity to about 24 hours. Longer wavelength UVA rays penetrate deeper into the skin than UVB, weakening inner skin tissue and accelerating skin aging.4 Artificial UVA radiation, used for cosmetic tanning, is as dangerous as its natural counterpart and is thought to be capable of inducing nonmelanoma skin cancer.5,6 Premalignant keratoses, but not cancers, have been observed in users of tanning beds.7 UV overexposure has also been shown to damage skin membranes and DNA as well as suppress the immune system.8,9,10 It is believed that the immune systems “T” cells can be suppressed from fighting melanoma target cells for up to 3 weeks following overexposure and sunburn. The long-term consequences of overexposure include skin cancer, photosensitivity and premature skin aging.
Controversy exists in the scientific and medical communities as to the most dangerous type of UV exposure. Although UVB rays are responsible for producing melanin and for thickening the skin's outer layer as protection against sun damage, it has been argued that UVB is more harmful than UVA because it damages cell DNA through formation of cyclobutane pyrimidine dimmers and 6-4 photoproducts. UVA radiation more weakly induces these forms of DNA damage through an oxidative pathway. UVA rays also penetrate more deeply than UVB rays, thus damaging the dermis, the innerlayer of skin that contains the blood vessels, hair follicles, and nerve endings, and ultimately accelerating skin aging. As detrimental effects are associated with each type, a filter capable of blocking both UVA and UVB is necessary for an effective sunscreen formulation.
It is generally agreed that UV radiation not only suppresses the immune response of cells in the skin, contributing to the development of skin cancers, but may also induce generalized immune suppression and have an important impact on how people tight off infectious diseases. In the mouse model of sun exposure, induction of antigen-specific suppression appears to be linked to Fas ligand (FasL). It was shown that normal mice acutely exposed to UV exhibited a profound suppression of both contact hypersensitivity and delayed type hypersensitivity (DTH) reactions and the development of transferable antigen-specific suppressor cells. These reactions were found to be lacking in FasL-deficient mice. Therefore, Fas/FasL interactions are essential for systemic UV-induced suppression of immune responses that involve host antigen presentation and suggest an interrelationship between UV-induced DNA damage and FasL in this phenomenon. The emerging picture is that UV-induced DNA damage disarms the immune system in a manner similar to that observed in immunologically privileged sites. Further studies by Hill and his colleagues demonstrated that FasL is responsible for the accumulation of p53 mutations in UV irradiated mice11. Therefore, there is an important need for broad spectrum sunscreen/sunblock formulations that are capable of significantly reducing the damages from UVA and UVB and prevent immunosuppression.